One method of manufacturing ophthalmic lenses, such as intraocular lenses and contact lenses, is by cast molding. Cast molding of contact lenses is well known. See, for example, Appleton, et al., U.S. Pat. No. 5,466,147, Morris, U.S. Pat. No. 6,405,993, and Dean, U.S. Pat. No. 6,732,993.
In a contact lens cast molding process, a single mold assembly for molding a single contact lens product includes a female mold section having a concave optical surface defining an anterior surface of a lens to be made, and a male mold section having a convex optical surface defining a posterior surface of the lens to be made. Thus, when the male and female mold sections are assembled together, a contact lens shaped cavity is formed between the concave surface of the female section and the convex surface of the male section.
A process for cast molding a lens is as follows. A polymerizable lens material, for example a monomeric material or other lens precursor material is placed on a concave surface of a contact lens mold section. This is usually done by dispensing a volume of a lens precursor material onto a mold half or mold section.
Once filled, a second mold section is placed in contact with the first mold section to form a lens shaped cavity containing the lens precursor material.
One type of coupling of the first mold section and second mold section utilizes an interference fit between the first and second mold sections. For example, the second mold section may be held in place relative to the first mold section by a pressure fit provided by a portion of the first mold section acting on a portion of the second mold section.
Another type of coupling is referred to as a point contact coupling. With point contact mold sections, the first and second mold sections are placed in contact with each other, and require an additional coupling mechanism to hold the two mold sections together. For example, two point contact mold sections can be held together by physically clamping the mold sections together. Or, two point contact mold sections can be held together by fusing a portion of the two mold sections together. For example, U.S. Pat. No. 5,759,318 describes the use of ultrasonic energy to secure two mold sections together.
The type of coupling used to form the contact lens mold assemblies often relates to the type of material used to produce the mold sections. For example, more elastic or flexible polymeric materials, such as relatively non-polar or hydrophobic polymeric resins, may be used to form interference fit mold sections. In comparison, more rigid or inflexible polymeric materials, such as relatively polar or hydrophilic polymeric materials, may be used to form point contact mold sections.
After closing the two mold sections to form a contact lens mold assembly, the contact lens precursor material is cured for example, by applying heat and/or light or other suitable polymerizing means to the filled mold assembly, thereby producing a polymerized contact lens product between the mold sections. The contact lens product is then removed from the mold sections. The contact lens product is often an unfinished contact lens which is subjected to one or more finishing steps, for example, conventional finishing steps such as extraction and/or hydration, to produce the final contact lens.
In the formation of silicone hydrogel contact lenses, the use of relatively hydrophilic polymeric resins or polar resins, such as Soarlite S (Nippon Gohsei Ltd., Japan), is beneficial in producing silicone hydrogel contact lenses with ophthalmically desirable surface wettabilities without requiring a surface treatment or polymeric internal wetting agent in the contact lens. One obstacle associated with cast molding processes involves maintaining the appropriate placement and fixation of the mold sections, particularly after the lens precursor material has been placed between the mold sections and prior to polymerization thereof. When ultrasonic energy is used to secure two mold sections together, opacification, pitting, or bubble formation in the lens cup (e.g., the region of the mold section containing the lens precursor material) may occur. Further, it may also be difficult to form a mold assembly in which the lens precursor material has a substantially uniform thickness, or in other words the lens does not have an undesired prism due to thickening of the lens precursor material at one region of the lens cup relative to another different region.
In addition, because of the potentially fragile nature of the polymerized contact lens product, the mold sections should be separable without causing breakage of or damage to the lens product.
Thus, more effective, more reliable methods and systems for manufacturing lenses, for example methods and systems for coupling mold sections during manufacturing of contact lenses, are needed.